Pore Size--a Key Property for Selective Toxin Removal in Blood Purification

Purpose: Extracorporeal blood purification systems based on combined membrane/adsorption technologies are used in acute liver failure to replace detoxification as well as to remove inflammatory mediators in sepsis patients. In addition to coating and chemical modification of the surface, pore size significantly controls the selectivity of adsorption materials.

Methods: This study addresses the adsorption of albumin bound liver toxins, cytokines, and representative plasma compounds on three adsorbents which differ only in pore size distribution. All three adsorbents are based on hydrophobic poly(styrene-divinylbenzene) copolymer matrices and have mean pore sizes of 15, 30, and 100 nm.

Results: The pores of adsorbents act as molecular sieves and prevent the entry of molecules that are larger than their molecular cut-off. The results of this study reveal that adsorbents based on styrene-divinylbenzene polymers with 15 nm pores are suitable for cytokine removal, and the same adsorbents with 30-40 nm pores are the best choice for the removal of albumin-bound toxins in the case of liver failure. Adsorbents with very large pores lack selectivity which leads to uncontrolled adsorption of all plasma proteins. Therefore, hydrophobic adsorbents with large pores offer inadequate plasma compatibility and do not fulfill the requirements for blood purification.

Conclusions: Biocompatibility and efficiency of adsorbents used for blood purification can improved by fine tuning of adsorbent surface pore distributions.